What To Know About Hot-Aisle, Cold-Aisle, And Chimney Data Center Containment Strategies

Containment systems are used in modern data centers to isolate the hot discharge air from the cooler supply air, managing cooling by separating the airflow. This separation of hot and cold can be achieved through either hot-aisle containment, cold-aisle containment, or chimney containment, and it is important for several reasons.

For one thing, it helps to reduce hot spots, which can cause server failures. Hot spots are caused by recirculation of air from the hot aisle to the cold aisle. When that path for airflow is minimized or eliminated, the servers will instead be forced to pull intake air from only the cold aisle.

Containment can also help maximize the cooling potential of existing air conditioning equipment, possibly eliminating or postponing the need for additional CRAC units as server loads increase. According to some recent studies, as much as 50 percent of airflow within a typical data center is wasted, bypassing the servers and going directly back to the CRAC units without providing any effective cooling. Containment reduces this bypass air, allowing an overall reduction in air supply to the space, saving fan energy.

Reducing hot spots and cooling air bypass can save energy, because it becomes possible to increase supply air and cooling water temperature set points. Equipment efficiencies and potential free cooling hours increase along with these supply temperatures.

Increasing Importance of Containment

Growing equipment power densities, as well as the desire to increase energy efficiency, have driven the need for more effective separation of the hot and cold areas within the data center. The concept of containment began with the introduction of hot-aisle, cold-aisle arrangements and the standardization of computer server design to a front-to-back airflow arrangement in the 1980s and '90s, which have since remained the industry standard for data center layout.

The hot-aisle, cold-aisle layout consists of orienting adjacent rows of equipment cabinets in a front-to-front configuration to avoid hot discharge air from one row blowing into the intake of the adjacent row. All supply air can then be supplied only into cold aisles, with return air pulled only from the hot aisles. In this way, mixing can be reduced by delivering cold air and returning hot air in separate locations.

The ability to minimize the mixing of hot and cold air that these initial semi-contained designs afforded was enough to deal with the lower densities in the early years of data center design, but didn't totally address the air balancing issues involved with dynamically changing computer loads and continual server layout changes. Now that high power densities and increased emphasis on energy efficiency are the norm, a new take on containment is in order.

Containment Strategies

Over the last several years, power demands, and hence cooling loads of IT equipment, have risen steadily as manufacturers have managed to pack more processing power into ever smaller spaces. At the same time, increased use of virtualization and cloud-based computing has increased the utilization rate and power draw of existing servers. IT managers require an effective means of optimizing performance, minimizing new infrastructure and keeping cooling costs down.

Containment strategies have naturally evolved to meet this need, providing data center engineers and IT managers alike with a new set of tools to meet the increased challenges that come with designing around high-density applications. Using physical barriers to segregate the cooler supply air from the hot discharge air, total containment can potentially increase the effectiveness of existing cooling equipment from 40 or 50 percent to as high as 80 or 90 percent efficiency.